1. Field of the Invention
The present invention relates to filters for fluids such as hydraulic oil, transformer oil and lubricating oil, and more particularly to a fluid filter having a fluid collector which prevents leakage of unfiltered fluid into the filtered fluid, a directional flow control element which prevents leakage of unfiltered fluid between two opposed pairs of filter elements into the centrally located flow path, and a sheath for preventing expansion of the filter elements due to water adsorption.
2. Description of the Prior Art
Fluid filters for removing dirt, common residue, abrasive particles, acid condensate, sludge and corrosive matter from fluid such as engine lubricating oil are well known in the art. These filters are usually packaged either as disposable cannisters, replaceable cartridges, or as containers for containing generally one or more filter elements which are formed with layers of tissue wound about an inner core. Inflow and outflow connections are provided at the container inlet and outlet ports. Fluid entering the container will flow freely to an intake end of each filter element where the fluid enters the filter element and then flows axially through each filter element in the interstices between the layers of filtered tissues so that the dirt and sludge is removed from the fluid by the tissue layers. The fluid exits the filter elements and is then directed by a fluid collector through passageways to a centrally located flow path which is connected to the outlet port.
Substantial compressive forces are exerted hydraulically on the tissue layers. These forces tend to compress and deform the filter elements, particularly at the end of each filter element where the filtered fluid exits into a collector. As disclosed in U.S. Pat. No. 4,017,400 to Schade, these collectors often have an annular portion which extends into the adjacent filter element ends to form a seal which separates the filtered fluid from the unfiltered fluid. Nevertheless, deformation of the filter element at its exit end may cause flow channels to form which then allow fluid to flow around the annular seal and thus entirely bypass the filter element. As a result, a significant amount of unfiltered fluid can pass around the deformed filter element without removal of contaminants.
A flexible, nonporous membrane has been placed in a sealing relation about the peripheries of the filter elements and around the collectors to prevent the fluid from entering the collector without first passing through at least one filter element. This flexible membrane is often formed from an elastic material such as neoprene. When water adsorption causes the filter elements to expand radially outwardly thereby greatly increasing the peripheries of the filter elements, the flexible membrane also expands and can eventually press against the inside wall of the filter container. Filter element replacement therefore becomes quite difficult because the membrane acts as a "brake" against the inside wall of the filtered container when the filter element is being removed.
Fluid collectors which are used for directing filtered fluid from the filter elements into the centrally located flow path often are utilized in combination with at least one screen which is placed between the collector and the adjacent filter element. The screen maintains the filter element in a spaced relation to the collector, so that a space is formed where filtered fluid is allowed to exit from the filter element into the collector. The hydraulic forces within the filter which deform the filter element often cause the tissue layers in the filter element to be pressed into the interstices of the screen, thereby partially inhibiting the flow of fluid from the filrer element into the collector. This may be particularly problematic in industrial applications where large fluid flows are often required.
Fluid filters sometimes have a plurality of filter elements which are arranged so that the intake ends of two filter elements face each other. These intake ends must be maintained in a spaced relation so that unfiltered fluid can enter both intake ends. Corrugated cardboard has been used to maintain the intake ends in such a spaced relation. The cardboard tends to restrict fluid flow into the filter element inlet ends while permitting unfiltered fluid to leak into the centrally located flow path. The unfiltered fluid often travels along between the filter element core and the centrally located flow path to receiving ports into the centrally located flow path, thereby entirely bypassing the filter element tissue layers.
Increasing costs for the disposal and replacement of lubricating, hydraulic and transformer fluids has created a need for a fluid filter which lengthens the effective life of these fluids by maintaining them in as clean a state as possible. It is therefore essential to prevent unfiltered fluid from bypassing the filter elements and contaminating the filtered fluid.